This invention relates to ultrasonic range finding.
It is well-known to measure range by measuring the transit time taken for an ultrasound pulse to travel to and return from a target. It is also known to employ a phase measuring method, as described in "Ultrasonic Testing of Materials" (J and H Krautkramer), Third Edition, Page 286. The known phase measuring method involves the use of continuous waves of constant frequency and comparing the phase displacement of the echo with respect to the transmitted signal. This necessarily entails the use of separate transmitters and receivers and, in addition, if the range is greater than one wavelength, the approximate distance must be known.